xfs: export max_open_zones in sysfs

Add a zoned group with an attribute for the maximum number of open zones.
This allows querying the open zones for data placement tests, or also
for placement aware applications that are in control of the entire
file system.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

Author: Christoph Hellwig

fs/xfs/xfs_mount.h

@@ -287,6 +287,7 @@ typedef struct xfs_mount {
 #ifdef CONFIG_XFS_ONLINE_SCRUB_STATS
 	struct xchk_stats	*m_scrub_stats;
 #endif
+	struct xfs_kobj		m_zoned_kobj;
 	xfs_agnumber_t		m_agfrotor;	/* last ag where space found */
 	atomic_t		m_agirotor;	/* last ag dir inode alloced */
 	atomic_t		m_rtgrotor;	/* last rtgroup rtpicked */

fs/xfs/xfs_sysfs.c

@@ -13,6 +13,7 @@
 #include "xfs_log.h"
 #include "xfs_log_priv.h"
 #include "xfs_mount.h"
+#include "xfs_zones.h"
 
 struct xfs_sysfs_attr {
 	struct attribute attr;
@@ -701,6 +702,34 @@ xfs_error_sysfs_init_class(
 	return error;
 }
 
+static inline struct xfs_mount *zoned_to_mp(struct kobject *kobj)
+{
+	return container_of(to_kobj(kobj), struct xfs_mount, m_zoned_kobj);
+}
+
+static ssize_t
+max_open_zones_show(
+	struct kobject		*kobj,
+	char			*buf)
+{
+	/* only report the open zones available for user data */
+	return sysfs_emit(buf, "%u\n",
+		zoned_to_mp(kobj)->m_max_open_zones - XFS_OPEN_GC_ZONES);
+}
+XFS_SYSFS_ATTR_RO(max_open_zones);
+
+static struct attribute *xfs_zoned_attrs[] = {
+	ATTR_LIST(max_open_zones),
+	NULL,
+};
+ATTRIBUTE_GROUPS(xfs_zoned);
+
+static const struct kobj_type xfs_zoned_ktype = {
+	.release = xfs_sysfs_release,
+	.sysfs_ops = &xfs_sysfs_ops,
+	.default_groups = xfs_zoned_groups,
+};
+
 int
 xfs_mount_sysfs_init(
 	struct xfs_mount	*mp)
@@ -741,6 +770,14 @@ xfs_mount_sysfs_init(
 	if (error)
 		goto out_remove_error_dir;
 
+	if (IS_ENABLED(CONFIG_XFS_RT) && xfs_has_zoned(mp)) {
+		/* .../xfs/<dev>/zoned/ */
+		error = xfs_sysfs_init(&mp->m_zoned_kobj, &xfs_zoned_ktype,
+					&mp->m_kobj, "zoned");
+		if (error)
+			goto out_remove_error_dir;
+	}
+
 	return 0;
 
 out_remove_error_dir:
@@ -759,6 +796,9 @@ xfs_mount_sysfs_del(
 	struct xfs_error_cfg	*cfg;
 	int			i, j;
 
+	if (IS_ENABLED(CONFIG_XFS_RT) && xfs_has_zoned(mp))
+		xfs_sysfs_del(&mp->m_zoned_kobj);
+
 	for (i = 0; i < XFS_ERR_CLASS_MAX; i++) {
 		for (j = 0; j < XFS_ERR_ERRNO_MAX; j++) {
 			cfg = &mp->m_error_cfg[i][j];